1. Field of the Invention
The present invention relates generally to apparatuses for filtering sewage and wastewater to remove fine impurities therefrom and, more particularly, to an apparatus for filtering sewage and wastewater that has a vertical structure, including a filtering belt comprising a filter bag or a filter mesh that can filter out fine impurities.
2. Description of the Related Art
Generally, filters are installed in sewage and wastewater inlet passages of sewage and wastewater disposal plants to filter out impurities, earth, sand, floating waste, etc. which are drawn into the inlet passages along with sewage and wastewater.
At present, to filter out impurities, earth, sand, floating waste, etc. that are drawn into the inlet passages of the sewage and wastewater plants, apparatuses for filtering sewage and wastewater, such as filter nets, auto-bar screens, step screens, vertical-screw screens, etc., have been used in the inlet passages. However, such conventional apparatuses are problematic in that it is difficult to filter out fine impurities, thin thread or fiber yarn shaped foreign substances (hair, strings), etc.
FIG. 1A is a side view of a conventional auto-bar screen. FIG. 1B is a view showing an embodiment of the installation of the auto-bar screen. The auto-bar screen is an apparatus that is most widely used and is operated in such a way that impurities that are filtered out when drawn sewage and wastewater passes through a screen part are taken out of the sewage and wastewater by a rake connected to a drive chain and then transferred into a collection container. The auto-bar screen is inexpensive, and installation cost thereof is comparatively low. However, it is difficult to filter out fine impurities, earth and sand. Hence, most impurities having thin and long shapes pass through the auto-bar screen and enter a sewage and waste water disposal plant, thus causing breakdown of equipment and a piping system that are used in the sewage and wastewater disposal plant.
Furthermore, when a sewage and wastewater inlet passage is deeper than from 4 m to 5 m underground, it is difficult to install the auto-bar screen. In cases where the auto-bar screen is installed at a comparatively deep position, a separate machine room is required, thus resulting in an increase in the installation cost.
FIG. 2A is a side view illustrating a conventional step screen. The step screen was proposed to mitigate the problems of the auto-bar screen. The step screen includes several tens of fixed lamellas and movable lamellas which are formed in a step shape. One movable lamella is placed between each fixed lamella, and the fixed lamellas and the movable lamellas are separately tied, thus forming two screens, that is, a fixed screen and a movable screen. FIG. 2B illustrates an embodiment of the lamellas of the step screen.
The step screen is superior to the auto-bar screen in a function of filtering out fine impurities. However, it still is not easy to filter out impurities of 1 mm or less or foreign substances, such as long fiber yarns. Furthermore, in cases where the step screen is installed in a sewage and wastewater inlet passage that is underground, the initial installation cost of the step screen increases, because a separate machine room is required.
FIG. 3 is a side view of a conventional vertical-screw screen, particularly, in which only a lower portion thereof is illustrated by a partially broken sectional view. In an effort to overcome the problem of the auto-bar screen or the step screen that requires a separate underground machine room, the vertical-screw screen was proposed. The vertical-screw screen is the same as that of a typical screw screen and is suitable for a limited underground place, such as a water passage under a manhole, which cannot have a screen room. However, in the case of the vertical-screw screen, because a gap between a cylindrical housing and a screw ranges 5 mm to 6 mm, impurities smaller than from 5 mm to 6 mm cannot be filtered out, and it is also difficult to filter out earth and sand.
FIG. 4 is a front view illustrating a conventional wedge drum screen. Unlike first stage equipment for wastewater treatment to remove solid bodies and sludge from industrial waste water or dishwater, or unlike conventional sieve screens or drum screens, the wedge drum screen has great performance in removing even fine particles depending on the size of the opening of a mesh.
However, in the case of the wedge drum screen, the cost of equipment is high, and a large impurity removal apparatus, such as an auto-bar screen or the like, must be installed ahead of the wedge drum screen to filter out large impurities. Furthermore, the wedge drum screen is disadvantageous in that it cannot be directly installed in a waste water inlet passage, so that when filtering inlet wastewater, a separate pump is required to pump inlet wastewater and supply it to the wedge drum screen.